Why are the repeat test results different?

Happy Holidays!

For a serious diagnosis like pheo, repeat testing of pheo markers is generally a good idea. Pheo test results from the same patient even within a few days or weeks can be quite different at times. Patients having acute illness, anxiety attack, or any emotional or physical stress would have higher pheo marker levels than when they are healthy and restful. The position (sitting or lying) of patients getting blood draw matters. Random variations are always possible. Laboratory errors do happen as well. If the two test results are concordant (which fortunately are more common), we can confidently say whether the patient has normal or abnormal pheo marker levels. If, however, the two test results are discordant (one abnormal and one normal, or one very high and one only slightly high), what shall we do?

There are several factors to consider. First, we need to see the quantitative differences between the two results. If one result is in the high normal range and the other slightly abnormal, they are essentially similar and concordant results. Second, we need to delve into the details on the patient’s mental and physical condition when the tests are done. If the patient is seriously ill when one test is taken, the result is likely higher and does not necessarily suggest pheo. Third, we need to ask ourselves the likelihood of this patient’s having pheo is high or not, based on the grounds why we test for pheo in the first place. Of course the more suspicion we have, the more likely the abnormal result is true. Fourth, past research has shown that if there are no laboratory errors, a single normal test result rules out pheo in most patients. Thus a negative pheo test result should be given more weight in general. Last, when we are really not sure, imaging is needed to give us more information.

Dr. Pheo

Ten years and going strong!

I started the Dr. Pheo blog on March 19, 2009. At that time, I was not certain how long the blog would last. Today, exactly 10 years later, I am pleased to see the blog is still going and going strong! I thank my family, friends, colleagues, patients, and especially readers for your support and encouragement in all these years.

      Pheo is a fascinating but challenging disease. In the last 10 years, we witnessed the explosive growth in pheo genetics and pathogenesis. Genetic tests for pheo are now widely available. We also observed the unraveling of the natural history of pheo and the understanding of pheo-induced heart problems. More doctors now recognize that small pheos exhibit features distinct from those of large pheos. The diagnosis of pheo progressed right in front of our eyes. Metanephrines are now accepted by most doctors as the best tests and are more available world-wide. The imaging characteristics of pheo were firmly established with the emergence of many nuclear imaging tools. In spite of the advancements, two major challenges still face us: misdiagnosis of pheo and management of malignant pheo.

      I will continue the blog as long as I can. I will remain anonymous.  

   

Dr. Pheo

Plasma or urine metanephrines?

I have discussed plasma versus urine metanephrines in the past. Recently a few doctors asked me this question again. I figure that if some doctors are not clear whether to order plasma or urine metanephrines, patients probably also want to know the pros and cons of plasma and urine metanephrines.

      First of all, both tests are great. If your local area only offers one of them, take it. If your local area offers both tests, which one is better? Shall you do both? My personal preference is plasma metanephrines. The plasma test is convenient and can be done to any patient at any time. The only small drawback is the blood draw itself. If you really hate needles, the plasma test could be an issue. The urine test offers no practical advantage over the plasma test. In theory and in earlier reports, the urine test is less prone to false positive results. In real clinical practice, the urine test and the plasma test perform similarly. The urine test is laborious to collect (24-hour urine is required), not reliable in patients with kidney problems, and hard to do in children. Lastly, the urine test results have to be corrected by urine creatinine. I have seen patients who passed ~5 liters of urine in 24 hours; of course the metanephrines levels are higher simply because of the large urine volume. The results usually are more accurate after they are divided by the total amount of creatinine in the urine. Again I want to emphasize that I personally don’t see why one would need the urine metanephrines for pheo diagnosis if plasma test is available. There is also no need to do both tests.

       

Dr. Pheo